This invention relates to a light projector such as a headlight for use with a vehicle.
The headlight for use with a vehicle is operated to light up under circumstances where a driver recognizes difficulty in seeing an area ahead of the vehicle with the unaided eye. The headlight is typically used in the nighttime, in a downpour of rain, in fog, or in other similar conditions. Actually, in some instances where the headlight is lit in a downpour of rain or in fog, an irradiated light beam diffuses by reflecting off raindrops and fine particles of water vapor, and the driver's view is obstructed by, as it were, a light wall standing in front of the vehicle.
A technique utilizing polarization for a headlight of a vehicle is disclosed in JP 61-253236 A. The invention as disclosed in this publication is directed to a technique for preventing a headlight providing a high beam from dazzling a driver. To be more specific, two polarizing filters are provided: one is provided in an optical path of the headlight for irradiating a high beam, and the other is stuck on a windshield, so that a polarization axis of the latter is perpendicular to that of the former. Accordingly, the high beam is cut off using the two polarizing filters (one on the windshield of the driver's vehicle, and the other in the headlight of oncoming vehicles), and the driver can thereby be prevented from being dazzled.
However, in the invention disclosed in JP 61-253236 A, disadvantageously, neither rain nor fog is envisaged as the problems to be addressed, and the use of polarizing filters would impair efficiency in utilization of light irradiated by the headlight. Moreover, the polarizing filter disadvantageously has low heat resistance (only up to 50° C.) in general, and thus attachment thereof to a headlight or the use in midsummer would significantly impair a polarizing capability thereof through the addition of heat derived from a lamp of the headlight or from sunbeams.